Aiming to study genesis and stability of submicron vesicles in biological samples we analysed small particles in samples derived from human blood and cultures of three marine microalgae: Tetraselmis chuii (T. chuii), Dunaliella tertiolecta (D. tertiolecta), and Phaeodactylum tricornutum (P. tricornutum). In blood and various blood plasma preparations obtained by centrifugation, and in isolates of small particles prepared from different blood fractions by differential centrifugation and ultracentrifugation we identified two mechanisms of small particle formation during sample processing – echinocyte transformation of erythrocytes with subsequent budding of vesicles from the tip of spicules, and fragmentation of platelets under the influence of shear forces during centrifugation. We developed a mathematical model to describe the dynamics of redistribution of particles in blood during centrifugation. This model allows a theoretical estimation of the optimal centrifugation time to obtain blood plasma with the highest possible concentration of platelets and small particles and their high recovery from the blood; and wherein the protocol can be adjusted for an individual blood sample, based on haemogram. In the microalgae T. chuii, D. tertiolecta and P. tricornutum, we identified three different mechanisms of formation of small particles found in isolates prepared by tangential flow filtration and by differential ultracentrifugation. These mechanisms include the shedding of flagella and the release of flagellar hairs and scales into the medium in T. chuii, the disintegration of undulating protrusions and flagella in D. tertiolecta and formation of virus-like nanoparticles in P. tricornutum. Using the dynamic light scattering method, we also assessed the solubilisation of the small particles in the isolates by surfactant Triton X-100, their stability in media with different osmolarity, and pH and their changes upon heating.
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